3.0 to 2.8 conversion

["Marc Jungo" <mjungo@domain.elided>]

Hello Alfisti,

It was suggested on the GTV6.org forum that instead of machining a
2.5 block, it might be possible to use a 3.0 block together with a
2.5 crank to obtain a 2.8 V6 (see topic "engine\difference between
2.5 and 3.0").
I know it might sound weird to plan to reduce the displacement of a
3.0, but I much prefer the feel and sound of the 2.5 (at least in a
GTV6, not necessarily in a 164), and it looks like it is mainly due
to its larger oversquareness, which would even be accentuated in a
2.8. Furthermore, I have a spare 3.0 with a toasted crank, which
makes a good starting point for such a project.
As far as I understand, the situation is as follows: 2.5 and 3.0
blocks are the same, except for the bore diameter. The rods are
identical and the 2.5 crank will fit in a 3.0. The pin is situated
at a higher position on the 3.0 piston, resulting in a lower
compression ratio (CR) if using standard 3.0 pistons on a 2.5 crank
(because of the reduced stroke). The solution might be to use either
custom-made pistons, or very high compression 3.0 pistons to reach a
reasonable CR value (I aim at a CR between 10 and 10.5).
So here are my questions:

*How can I figure out the actual CR resulting from the reduced stroke
(i.e. assuming I would use 11.5 pistons on the 2.5 crank with 3.0 heads)?
*Where can I find high compression 3.0 pistons (preferably not custom made).
*I have heard somewhere that Venolia makes a set of 2.8 liners and
pistons in 10.5 CR. Do someone have more information about that (pin
height, price, availability,...)?
*Can I use the 2.5 flywheel (together with the crank) in the 3.0? It
was mentioned in the GTV6 forum that the 3.0 block is shorter and
needs a different flywheel? I have a late '86 2.5, and a 3.0 from an
early 75/Milano (L-Jet). Do I need other parts?
*Is there something important I am missing?!?

Thank you in advance for your help!
Cheers, marc


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